import matplotlib as mpl
import matplotlib.pyplot as plt

mpl.rcParams['legend.handlelength'] = 0
mpl.rcParams['legend.markerscale'] = 0

fig, ax = plt.subplots()

ax.errorbar(x=[0.3], y=[0.7], xerr=[0.2], marker='+', markersize=10, label='horizontal marker')
ax.errorbar(x=[0.7], y=[0.3], yerr=[0.2], marker='+', markersize=10, label='is gone')

ax.set_xlim([0,1])
ax.set_ylim([0,1])
ax.legend(numpoints=1)
plt.show()